1. Field of the Invention
The present invention relates to a corneal surgical apparatus for incising the cornea of an eye of a patient in a layered form at the time of a keratorefrative surgery or the like.
2. Description of the Related Art
In recent years, attention has been focused on a LASIK surgery (laser in situ keratomileusis) for the keratorefrative surgery wherein a flap is formed by incising a portion with a thickness of about 0.15 mm from the corneal epithelium to the corneal stroma with a part of the cornea remaining connected like a hinge, ablating the corneal stroma in a refractive correction amount by an excimer laser light, and returning the flap to its original position. In the LASIK surgery, a corneal surgical apparatus called microkeratome is used for incising the cornea in a layered form.
As a corneal surgical apparatus, one comprising a suction ring to be vacuum-fixed to a part of the cornea from a corneal ring portion to the surface of the conjunctiva, a cornea applanating member for applanating the cornea flatly, and a blade movable toward the hinge while being oscillated laterally so as to incise the flattened cornea into a layer form with a substantially uniform thickness, is known.
As a mechanism for the blade lateral oscillation, as shown in FIG. 13A, one comprising a rotation shaft 301 to be rotated by a driving device such as a motor, an eccentric pin 302 provided at the tip end of the shaft 301, a transmitting member 304 having a vertical groove 303 to be engaged with the pin 302 is proposed. The transmitting member 304 having a blade 300 fixed thereto is held movably in the lateral direction (right and left direction, that is, the direction perpendicular to the paper surface in FIG. 13) in a receiving groove formed in a blade holder 305 and a holder block 306. When the shaft 301 is rotated by drive of the motor, force is applied on the transmitting member 304 in the lateral direction according to the circumferential movement (circular motion) of the pin 302 engaged with the vertical groove 303. Accordingly, the transmitting member 304 oscillated laterally (moved in the right and left direction), and further, the blade 300 fixed to the transmitting member 304 is oscillated laterally as well.
However, according to the conventional mechanism, as shown in FIG. 13B, by the circumferential movement of the pin 302, not only the force in the lateral direction but also force in the vertical direction (up and down direction) is applied to the transmitting member 304. That is, since the pin 302 with the circumferential movement comes in contact with the wall of the vertical groove 303 so that force is applied on the transmitting member 304 in the vertical direction due to the friction force generated by the contact, the transmitting member 304 is oscillated laterally while being moved also in the vertical direction. Therefore, if the shaft 301 is rotated at a high speed, the transmitting member 304 and the blade 300 generate vertical oscillation (up and down movement) called "rampage" in addition to the lateral oscillation.
The "rampage" hinders stable incision as well as generates a loss in terms of the efficiency of converting the rotational motion to the lateral oscillation. Moreover, since the corner part of the transmitting member 304 is contacted with a blade holder 305 and the holder block 306 frequently so as to be applied with a large force, the parts are worn out rapidly so that the life cycle thereof is shortened.
The displacement amount of the transmitting member 304 to be displaced vertically and laterally (in the up and down, and right and left directions) according to the circumferential movement of the pin 302 corresponds to the eccentric amount of the pin 302, but as to the vertical direction, since the transmitting member 304 is held by the blade holder 305 and the holder block 306 in the vertical direction, the transmitting member 304 (and the blade 300) is displaced (vertical oscillation) for the gap with respect to each member. Therefore, accurate production without a gap among the transmitting member 304, the blade holder 305 and the holder block 306 would prevent the vertical oscillation (that is, "rampage"), however, much labor is required for meeting the demand particularly in mass production so as to increase the cost.